Why do python list slices extend beyond the length of a list?

Question

I was trying to use list slices earlier in python, and came across a strange case where I was expecting a particular list slice to cause an error.

Take for instance a list, a, with the following elements.

>>> a = [1,2,3,4]
>>> a[0:4]
>>> [1,2,3,4]

Furthermore, using the correct index removes an element

>>> a[0:3]
>>> [1,2,3]

Can someone make this make sense please? This is making use of list slices quite confusing.

This makes some things easy to write like e. g. "a[0:2] + [7] + a[2:]" to create a new list with inserted item 7 at position 2. — Michael Butscher, Aug 08 '22 at 19:50

score 3 · Answer 1 · answered Aug 08 '22 at 19:47

3

The second index is exclusive, meaning the last element the slice will return is the one in front of the specified index. Thus, in your example [0:4] returns elements in indices 0 to 3.

answered Aug 08 '22 at 19:47

Filip Müller

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Why do python list slices extend beyond the length of a list?

1 Answers1